EP2537664A1 - Method and machine for the manufacturing of containers allowing a modification of a heating rate - Google Patents

Abstract

Machine (1) for the manufacture of containers (2) from blanks (3) of plastic, which comprises an oven (4) provided with a plurality of sources (8) of radiation, for heating at the parade of blanks (3) at a predetermined speed and a predetermined heating profile, and a central control (9) programmed to make a change in the running speed and the heating profile according to a temperature measurement made on a blank (3) at the outlet of the oven (4), and a measurement of pressure performed in said blank (3) during a subsequent blowing.

Description

The invention relates to the manufacture of containers, in particular bottles, flasks, by forming from blanks (generally preforms, although they may be intermediate containers) made of plastic such as polyethylene terephthalate (PET) .

The manufacture of a container comprises two main phases, namely a heating phase of the blank, during which the blank passes through a heating unit, followed by a blowing phase during which the thus heated blank is transferred to a molding unit, and a pressurized fluid (usually a gas, usually air) is injected into the blank to give it the final shape of the container.

In the heating unit (commonly called "furnace"), the blanks pass in front of a row of sources of infrared radiation - generally halogen lamps - at a predetermined speed of movement and heating profile.

The speed of travel of the furnace is the linear velocity at which the preforms, which are attached to rotating supports or "spinners" mounted on a chain driven in motion by a toothed wheel, hang. Each spin is secured to a pinion meshing a rack to drive the preform in rotation about its axis during its movement.

• la puissance du rayonnement infrarouge émis par les sources, qui détermine la quantité totale d'énergie injectée dans le four ;
• la topographie du four, et notamment la présence de réflecteurs en regard des sources, qui détermine une quantité d'énergie non absorbée directement par les ébauches mais réinjectée dans le four par réflexion ;
• le débit de la ventilation forcée des ébauches, qui détermine une quantité d'énergie évacuée du four.

The heating profile, that is to say the profile of the amount of energy actually received by the blanks in the oven during the heating phase, is mainly determined by three controllable heating parameters:

• the power of the infrared radiation emitted by the sources, which determines the total amount of energy injected into the furnace;
• the topography of the furnace, and in particular the presence of reflectors facing sources, which determines a quantity of energy not absorbed directly by the blanks but reinjected into the furnace by reflection;
• the rate of forced ventilation of the blanks, which determines a quantity of energy removed from the oven.

Furnace structures are described in particular in the SIDEL patents FR 2 703 944 , FR 2,907,684 , FR 2 863 932 (and in their respective US counterparts US 5,681,521 , US 2009/317506 , US 7,553,156 ).

The heating and blowing units are generally part of a production line which also comprises a filling unit (or filler), associated with a closure unit, as well as possibly a labeling unit and a package unit ( for example a shrinkwrapper).

On any production line there is a critical machine, which imposes its pace on the whole line. In this case, the critical machine is the filler.

To compensate for the differences in the speed of the different machines, buffer stocks are formed between them, by means of accumulation conveyors whose capacity is generally adjustable to allow an adaptation of the stock to variations of pace.

But the accumulation conveyors are expensive and bulky, and it would be theoretically more profitable to vary the rate of each machine to adapt to the rate of the critical machine.

In practice, however, if we can indeed, for some machines (including the blowing unit), vary the rate (in a limited way, of the order of a few%) - without affecting the quality of production, some machines are not designed to support such variation. This is particularly the case of the oven which, once reached its steady state, can not see its rate vary during production, except to admit an uncontrolled drift of the quality of the containers produced.

To date, the specialized operators in charge of the furnaces apply for each production range a standardized heating profile according to the type of blank to be heated, and a heating rate (that is to say a speed constant preform) determined by the rate of production imposed by the critical machine. If the operators can apply specific manual corrections to the heating parameters, depending on the perceived subjective quality of the containers, the risks of uncontrolled drift in the quality of the containers produced are too great for the operators to be given the freedom to change the rate of the oven. In fact, in practice the rate of the oven is stationary steady.

The invention aims to allow a modification (which can be substantial) of the heating rate, maintaining the quality standard of production.

• une phase de chauffe des ébauches au défilé, dans un four muni d'une pluralité de sources de rayonnement, à une vitesse de défilement et selon un profil de chauffe prédéterminés ;
• une phase de soufflage des ébauches, au sein d'une unité de soufflage, pour former les récipients,

ce procédé comprenant les opérations consistant à :

1. a) modifier la vitesse de défilement des ébauches ;
2. b) modifier le profil de chauffe ;
3. c) établir, à l'issue d'une phase de chauffe, un profil thermique réel d'au moins une ébauche ;
4. d) effectuer, lors de la phase de soufflage, une mesure de pression dans ladite ébauche et détecter au moins un point singulier de pression ;
5. e) mesurer un premier écart entre le profil thermique réel de l'ébauche et un profil thermique théorique, et un deuxième écart entre le point singulier de pression et un point singulier théorique ;
6. f) tant que les écarts ne sont pas tous deux inférieurs à une tolérance prédéterminée respective, répéter les opérations b) à e) ;
7. g) tant que les écarts sont tous deux inférieurs à la tolérance respective, et tant que la vitesse de défilement n'a pas atteint une valeur finale prédéterminée, répéter les opérations a) à e).

For this purpose, it is proposed, in the first place, a method of manufacturing containers from plastic blanks, which comprises:

• a phase of heating the blanks to the parade, in a furnace provided with a plurality of radiation sources, at a running speed and according to a predetermined heating profile;
• a phase of blowing the blanks, within a blowing unit, to form the containers,

this process comprising the steps of:

1. a) change the speed of scrolling of the blanks;
2. b) modify the heating profile;
3. c) establishing, after a heating phase, a real thermal profile of at least one blank;
4. d) performing, during the blowing phase, a pressure measurement in said blank and detecting at least one singular point of pressure;
5. e) measuring a first difference between the real thermal profile of the blank and a theoretical thermal profile, and a second difference between the singular point of pressure and a theoretical singular point;
6. f) as long as the deviations are not both less than a respective predetermined tolerance, repeat steps b) to e);
7. (g) as long as the deviations are both less than the respective tolerance, and as long as the running speed has not reached a predetermined final value, repeat steps a) to e).

• le profil thermique comprend une thermographie de l'ébauche ;
• le profil thermique comprend une mesure de température effectuée sur une paroi externe de l'ébauche ;
• le profil thermique comprend une mesure de température effectuée sur une paroi interne de l'ébauche ;
• le point singulier de pression est un pic local de pression ;
• le profil de chauffe comprend une puissance électrique délivrée aux sources de rayonnement ;
• le profil de chauffe comprend une puissance électrique délivrée à un système de ventilation du four.

Various additional features of this process may be provided, alone or in combination:

• the thermal profile includes a thermography of the blank;
• the thermal profile comprises a temperature measurement performed on an outer wall of the blank;
• the thermal profile comprises a temperature measurement performed on an inner wall of the blank;
• the singular point of pressure is a local peak of pressure;
• the heating profile comprises an electric power delivered to the radiation sources;
• the heating profile includes an electric power delivered to a ventilation system of the oven.

It is proposed, secondly, a computer program product intended to be stored in memory of a processing unit and / or stored on a memory medium readable by a reader of a processing unit, comprising instructions for implementation of operations a) to g) of the method described above.

It is proposed, thirdly, a machine for the manufacture of containers from plastic blanks, which comprises an oven provided with a plurality of radiation sources, for heating the parade drafts at a scrolling speed and according to a predetermined heating profile, and a control unit programmed to make a change in the running speed and the heating profile as a function of a temperature measurement made on a blank at the outlet of the oven, and a measurement pressure carried in said blank during a subsequent blowing.

• la centrale de commande est programmée pour modifier une puissance électrique délivrée aux sources ;
• la centrale de commande est programmée pour modifier une puissance électrique délivrée à un système de ventilation du four.

Various additional features of this machine may be provided, alone or in combination:

• the control unit is programmed to modify an electrical power delivered to the sources;
• the control unit is programmed to modify an electrical power delivered to a ventilation system of the oven.

• la figure 1 est une vue schématique en plan montrant une machine de fabrication de récipients comprenant une unité de chauffe d'ébauches et une unité de soufflage de récipients à partir des ébauches chauffées ;
• la figure 2 est une vue schématique en coupe montrant partiellement la machine de la figure 1 ;
• la figure 3 est un diagramme fonctionnel illustrant différentes étapes d'une modification contrôlée de la cadence de chauffe ;
• la figure 4 est un diagramme sur lequel sont tracées des courbes illustrant des paramètres de chauffe et de soufflage.

Other objects and advantages of the invention will become apparent in the light of the description given hereinafter with reference to the appended drawings in which:

• the figure 1 is a schematic plan view showing a container making machine comprising a blanking unit and a container blowing unit from the heated blanks;
• the figure 2 is a schematic sectional view partially showing the machine of the figure 1 ;
• the figure 3 is a functional diagram illustrating different steps of a controlled change in the rate of heating;
• the figure 4 is a diagram on which curves are drawn showing heating and blowing parameters.

On the figures 1 and 2 is schematically shown a machine 1 for manufacturing containers 2 from blanks 3 (it is in this case preforms) of plastic such as PET. This machine 1 comprises a heating unit 4 , also called "furnace", and a molding unit 5 provided with a series of molds 6 mounted on a carousel and placed directly downstream of the furnace 4.

The preforms 3 are conveyed through the oven 4 to be heated prior to the blowing or stretching operations taking place within the molding unit 5 . For this purpose, the furnace 4 is equipped with a first emitting wall 7 provided with sources 8 of electromagnetic radiation emitting on a spectrum (in the field of the infrared or, possibly, in the range of microwaves) and at a predetermined power. . Typically, sources 8 of radiation emitting in the infrared range may be lamps (such as halogen lamps, as in the example shown in FIG. figure 2 ) or diodes, such as laser diodes, for example of the surface-emitting vertical cavity type (VCSEL). The electrical power, denoted P _S , supplied to the sources, as well as the spectrum of the emitted radiation, are controlled by means of a programmable control unit 9 . Conventionally, the furnace 4 comprises, facing the emitting wall 7 , a second reflecting wall 10 , providing at least partial reflection of the radiation emitted by the sources 8, so as to limit losses by dissipation and thus optimize the heating .

Each preform 3 is attached to a rotary hanger 11, also called spin, which comprises a pin 12 fitted in a neck 13 of the preform 3, and a pinion 14 meshing with a fixed chain 15 running along the path followed by the preforms 3 in the furnace 4. This conveying mode ensures a substantially uniform rotation of the preform 3 during its heating. It should be noted that the conveying of the preforms 3 can equally well be ensured at the bottom 13 (as in the example shown) or at the top 13 . Each spinner 11 is rotated about an axis 16 integral with a belt 17 driven in displacement by a wheel 18 whose engine is controlled by the control unit 9 , at a speed V predetermined linear scroll which is stationary steady state. Since the spacing between the preforms 3 is fixed, the production rate (that is to say, in practice, the quantity of preforms 3 leaving furnace 4 for a predetermined duration, generally 1 h) is directly proportional to the speed V scrolling.

The preforms 3 are heated in such a way that the preforms 3 have, at the furnace outlet 4, an average heating temperature greater than the glass transition temperature of the material. Typically, the average heating temperature is about 140 ° C for PET preforms 3 whose glass transition temperature is about 80 ° C. The transit of the preforms 3 between the outlet of the furnace 4 and the inlet of the molding unit 5 is sufficiently short that the cooling of the preforms 3 by heat dissipation is negligible.

According to one embodiment, (especially in the case where, as illustrated on the figure 2 the sources 8 are halogen lamps, heat dissipators), the oven 4 comprises a forced ventilation system 19 in the form of a blower generating a pulsed air flow directed towards the preforms 3 flowing in the oven 4, in order to evacuate some of the calories. The blower 19 is controlled by the control unit 9 , which controls the electrical power, denoted P _V , delivered to the blower 19 (and therefore the flow rate of the air flow generated).

The electrical power P _S supplied to the sources 8, the power P _V supplied to the blower 19 and the speed V of the preforms 3 are all three controlled by the control unit, which is programmed accordingly.

In order to adapt the production rate of the furnace 4 to a variation of the rate of a critical machine (for example a filling unit) situated on the same production line, it is desired to introduce a modification of the scrolling speed V, to increase it (increase of pace), either on the contrary to reduce it (decrease of rate), while preserving the quality of the containers 2 at the exit of the unit 5 of molding.

The modification of the speed V scrolling changing the exposure time of the preforms 3 to the radiation ensuring their heating, this modification requires a change in the heating profile if one wishes to maintain the quality of the containers 2.

Experience shows that the quality of the container 2 largely depends on the temperature profile of the preform 3 leaving the oven 4. In particular, a too low temperature of the preform 3 can induce on the container 2 the appearance of a Pearly appearance (pearlescent aspect) whitish, consequence of an overetching of the preform 3 causing at the molecular level a break in the long polymerized chains. On the other hand, an excessively high temperature of the preform 3 may cause spherulitic crystallization of the material, rendering the preform 3 unsuitable for blowing.

It has therefore been determined that any preform 3 coming out of the furnace 4 must have a real thermal profile corresponding to a predetermined theoretical profile for which the quality of the container 2 is optimal. This does not necessarily mean that the actual thermal profile must be strictly equal to the theoretical profile, which in practice is impossible to obtain, but that the actual thermal profile must have, compared with the theoretical profile, a deviation below a certain tolerance that can be determined by those skilled in the art by conducting ordinary tests, and for which the quality of the containers 2 obtained is in accordance with the requirements of the bottler.

The thermal profile can be reduced to a single measurement of average temperature, performed by means of a thermal sensor disposed at the outlet of the oven 4. Preferably, however, the thermal profile comprises a plurality of temperature measurements made on a body 20 of the preform 3, in particular on an outer wall 21 and / or on an inner wall 22 thereof.

According to an exemplary embodiment illustrated on the figure 2 , the thermal profile comprises a thermography of the outer wall 21 on all or part of the body 20, made by means of a thermal camera 23 (infrared) connected to the control unit 9, to which the thermographic data are communicated by the camera 23.

According to another exemplary embodiment, the thermal profile comprises a temperature measurement or a thermography performed on the internal wall 22 , which can be carried out in accordance with the description of the French patent application no. FR 2 935 924 or its international counterpart WO 2010/031923 , the contents of which are hereby incorporated by reference.

It has been determined, however, that if the control of the thermal profile of the preforms 3 is necessary to maintain the final quality of the containers 2 produced, it is not sufficient. Tests have indeed shown that with substantially identical thermal profiles, and with equal mechanical characteristics (the preforms 3 may in fact have defects in shape or material), two preforms 3 can lead to containers 2 of unequal quality.

Feedback on the heating parameters (P _S and P _V ) based solely on the thermal profile of the preforms 3 leaving the oven 4 has in fact proved insufficient to control the quality of the containers 2.

Tests have, however, shown that, taking into account both the thermal profile and the evolution of the pressure in the preform 3 during blowing, it is possible to effectively feedback on the heating parameters in order to control the quality of the containers 2.

More precisely, without it being necessary to take into account the pressure curve as a whole, it has proved sufficient to take into account at least one singular point on this curve.

In practice, it has even proved sufficient to take into account a local pressure peak during a pre-blowing operation, corresponding to the plastic flow threshold of the preform 3, from which the radial expansion of the in the mold 6.

The characteristics of this point, called point B, and its importance on the quality of the container 2, have been presented in French patent application no. FR 2 909 305 (or in its international equivalent WO 2008/081108 ).

It may seem that point B does not provide any additional information, compared to the only thermal profile of the preform 3 at the outlet of the oven 4. Indeed, it is accepted that the position of the point B is influenced by the temperature heating means of the preform 3: roughly, an increase in the temperature induces an anticipation of the instant t _B of occurrence of the point B, and a decrease of the corresponding pressure P _B ; on the other hand, a decrease in the temperature theoretically induces a delay of the instant _B of occurrence of the point B, and an increase in the corresponding pressure P _B. These statements are correct if we consider an average temperature.

In fact, the heating profile of the preform 3 and the point B do not provide two redundant but complementary information as to the intrinsic characteristics of the preform 3, making it possible to evaluate its adequacy with a satisfactory theoretical model.

The hypothesis invoked to justify this observation is that, with a similar temperature profile, minute temperature variations, either that can not be measured, or that it would be too restrictive to take into account, can significantly affect the quality. blowing, whose experience has shown that point B is a reliable - and measurable - indicator.

• du profil de température de la préforme 3 à la sortie du four 4,
• et d'un point singulier de pression dans la préforme pendant le soufflage (en l'occurrence le point B),

permet d'effectuer une rétroaction fiable sur le profil de chauffe, de manière à maintenir la qualité des récipients 3 lors d'une modification de la cadence du four 4. So that taking into account both:

• of the temperature profile of the preform 3 at the outlet of the oven 4,
• and a singular point of pressure in the preform during blowing (in this case point B),

allows a reliable feedback on the heating profile, so as to maintain the quality of the containers 3 during a change in the rate of the oven 4.

The pressure measurement in the container 2 can be carried out by means of a pressure sensor 24 mounted for example (as shown in FIG. figure 2 ) in a nozzle 25 for injecting fluid into the preform 3, capping the mold 6 during blowing, and connected to the control unit 9 to which the sensor 24 communicates its measurements.

The manufacture of the containers 2 from the preforms 3 comprises two main phases, namely a heating phase of the preforms 3 to the parade in the furnace 4, at a predetermined speed V and according to a heating profile, and a consecutive phase of blowing the preforms 3, within the blowing unit 5 , each preform 3 being introduced into a mold 6 as illustrated in FIGS. figures 1 and 2 .

The scrolling speed V and the heating profile (characterized by the power P _S delivered to the sources 8 and the power P _V delivered to the fan 19) are programmed in (and controlled by) the control unit 8 .

From an initial running speed V _i , the operating mode for modifying this speed to reach a final speed V _F is now described. This procedure is illustrated on the figure 3 .

1. a) une modification de la vitesse V de défilement et
2. b) une modification du profil de chauffe,

ce de manière simultanée ou quasi-simultanée.The control unit starts by piloting:

1. a) a modification of the speed V of scrolling and
2. b) a modification of the heating profile,

this simultaneously or almost simultaneously.

The modifications introduced are incremental and correspond to a percentage only of the final modification aimed at (less than 10%, and preferably less than 5% of the difference between the initial value and the final value of the modified parameter). In simplified terms, the speed V is incremented by a variation δV (positive or negative), the modified speed being equal to V + δV. Similarly, the power P _S delivered to the sources 8 and / or the power P _V delivered to the fan 19 are incremented by a respective variation δP _S or ΔP _V (positive or negative), the power P _S or P _V modified being equal to P _S + δP _S or respectively to P _V + ΔP _V.

Specifically, the modification of the speed V of travel can be performed by varying the speed of rotation of the driving wheel 18 on which the belt 17 driving the preforms 3.

• c) à l'établissement, à la sortie du four 4 et à l'issue d'une phase complète de chauffe, d'un profil thermique réel d'au moins une préforme 3 (ou d'une sélection de préformes 3 ou encore, de préférence, de toutes les préformes 3) entrée(s) dans le four 4 après la modification de la vitesse V de défilement et du profil de chauffe, puis
• d) lors de la phase de soufflage, à une mesure de pression dans cette (ou ces) préforme(s) 3.

Following this first modification, we proceed then:

• c) at the establishment, at the exit of the furnace 4 and at the end of a complete heating phase, a real thermal profile of at least one preform 3 (or a selection of preforms 3 or preferably, all the preforms 3) entered into furnace 4 after the modification of the scrolling speed V and the heating profile, and then
• d) during the blowing phase, to a pressure measurement in this (or these) preform (s) 3.

The thermal profile is measured by means of the thermal camera 23 , the result being a curve (or a cloud of points) corresponding to the variations of the temperature T along a function f of the axial coordinate (or altitude, denoted Z) where the measurement is carried out on the preform 3, considering (which corresponds to the majority of the cases, apart from the case of the preferential heating intended for the manufacture of non-symmetrical containers of revolution) that at constant altitude the temperature T is constant. The temperature profile is therefore provided by the curve T = f (Z).

The pressure measurement is carried out by means of the pressure sensor, the result being a curve (or a cloud of points) corresponding to the variations of the pressure P along a function f of the time t elapsed since the introduction of the preform 3 into the mold 6: P = g (t).

• e) mesurer un premier écart δT entre le profil thermique réel de la préforme 3 et le profil thermique théorique en mémoire ; mesurer un deuxième écart δB entre le point singulier réel de pression (point B réel) et le point singulier théorique en mémoire (point B théorique).

The measurements T and P are communicated continuously to the control unit 9 . The latter acquires the data, makes a respective comparison of the actual temperature profile with the stored theoretical profile, and detects in the pressure curve the programmed singular point (in this case point B). Control unit 9 then performs the following operations:

• e) measuring a first difference δT between the real thermal profile of the preform 3 and the theoretical thermal profile in memory; measure a second difference δB between the actual singular point of pressure (real point B) and the theoretical singular point in memory (theoretical point B).

The difference δB between the real point B and the theoretical point B can indifferently be a difference ΔP _B in the value of the pressure at point B, or a deviation δt _B in the value of the instant t _B of occurrence of the point B.

• f) comparer l'écart δT de profil thermique avec une tolérance S_T prédéterminée (mémorisée dans la centrale), et comparer l'écart δB (δP_B et/ou δt_B) avec une tolérance prédéterminée S_B (de pression et/ou de temps) également en mémoire.

The control unit 9 then performs the operation of:

• f) comparing the deviation δT of the thermal profile with a predetermined tolerance S _T (stored in the control unit), and comparing the deviation δB (ΔP _B and / or δt _B ) with a predetermined tolerance S _B (of pressure and / or of time) also in memory.

If the differences δT and δB are not both less than their respective tolerance S _T and S _B , which means that a drift is noted in the quality of the preforms 3, then the control unit 9 controls a repetition of the operations b) to e) to correct the heating profile by iteration until the deviations δT and δB are within the expected tolerances.

As long as the deviations δT and δB are within the expected tolerances S _T and S _B , and until the final value V _F is reached, the control unit 9 controls a repetition of the operations a) to e), that is ie a repetition of the rate change and heating profile operations.

The operations described above may be implemented by instructions of a computer program implemented in a processor of the control panel 9 , or on an external medium (type CD-ROM) readable by it.

• la courbe illustrant la variation de la vitesse V de défilement,
• la courbe illustrant la variation de la puissance P_S électrique fournie aux sources 8, et
• la courbe illustrant la variation de la puissance P_V électrique fournie à la soufflerie 19.

We have illustrated on the diagram of the figure 4 two successive modifications of cadence: firstly, starting from a high speed V ₁ , a reduction of the speed V to a low speed V ₂ (V _i = V ₁ , V _F = V ₂ ), then vice versa , starting from the low speed V ₂ , an increase in the speed V to the high speed V ₁ (V _i = V ₂ , V _F = V ₁ ). We have drawn on the diagram:

• the curve illustrating the variation of the scrolling speed V,
• the curve illustrating the variation of the electric power P _S supplied to the sources 8 , and
• the curve illustrating the variation of the electrical power P _V delivered to the wind tunnel 19 .

For simplicity, a linear and continuous reduction of the speed V is shown. On the other hand, the slot variations of the powers P _S and P _V illustrate the modifications of these parameters by successive iterations (δP _S and ΔP _V ), controlled by the central 9 as and when changes in pace. The diagram shows that the process is reversible. During the first rate change, the power P _S decreases in successive stages from a high value P _S1 to a low value P _S2 ; then, during the second rate change, the power P _S increases in successive stages from the low value P _S2 to the high value P _S1 . At the same time, the power P _V first increases in successive stages from a low value P _S1 to a high value P _V2 ; then, during the second rate change, the power P _V decreases in successive stages from the high value P _V2 to the low value P _V1 .

It has been found that the modification of only the power parameters P _S delivered to the sources and the power P _V delivered to the ventilation system is sufficient to maintain the quality of the containers 2 during a change in the rate of the oven 4 .

This finding can be explained in the following theory.

As a first approximation, the quantity of energy E _P actually absorbed by the preforms 3 in the furnace 4 is equal to the quantity of energy E _S emitted by the sources 8, minus the quantity of energy E _V evacuated from the oven 4 by the ventilation 19 and the amount of energy E _F absorbed by the components of the furnace 4 itself, which undergo a heating: $${\mathrm{E}}_{\mathrm{P}}\mathrm{\approx }{\mathrm{E}}_{\mathrm{S}}\mathrm{-}{\mathrm{E}}_{\mathrm{V}}\mathrm{-}{\mathrm{E}}_{\mathrm{F}}$$

It is reasonable to estimate that the amount of energy E _F absorbed by the components of the furnace 4 is negligible in view of the fact that the great majority of the components subjected to the radiation are reflectors which absorb only a small part of the radiation that they receive, the essential being reflected towards the preforms 2.

Thus, in a second approximation, the quantity of energy E _P actually absorbed by the preforms 3 in the furnace 4 is substantially equal to the quantity of energy E _S emitted by the sources 8, minus the quantity of energy E _V evacuated from the oven 4 by the blower 19: $${\mathrm{E}}_{\mathrm{P}}\mathrm{\approx }{\mathrm{E}}_{\mathrm{V}}\mathrm{-}{\mathrm{E}}_{\mathrm{E}}$$

• la quantité d'énergie E_S émise par les sources 8 est proportionnelle à la puissance électrique P_S absorbée, en admettant que leur rendement est constant : E_S ≈ K1·P_S, où K1 est une constante positive ;
• la quantité d'énergie E_V évacuée du four 4 par la soufflerie 19 est proportionnelle à la fois à la puissance électrique P_V absorbée par la soufflerie 19 et à la quantité d'énergie E_S émise par les sources 8 (c'est-à-dire à la puissance électrique P_S absorbée par les sources 8) : E_V ≈ K2·P_S·P_V, où K2 est une constante positive.

Moreover, it is estimated, according to a good approximation, that:

• the quantity of energy E _S emitted by the sources 8 is proportional to the electrical power P _S absorbed, assuming that their efficiency is constant: E _S ≈ K1 · P _S , where K1 is a positive constant;
• the quantity of energy E _V discharged from the furnace 4 by the blower 19 is proportional to both the electrical power P _V absorbed by the blower 19 and the quantity of energy E _S emitted by the sources 8 (that is, that is, the electrical power P _S absorbed by the sources 8): E _V ≈ K2 · P _S · P _V , where K2 is a positive constant.

So that the amount of energy E _P actually absorbed by the preforms 3 can be expressed as follows: $${\mathrm{E}}_{\mathrm{P}}\mathrm{\approx }\left(\mathrm{K}\mathrm{1}\mathrm{\cdot }\mathrm{-}\mathrm{K}\mathrm{2}\mathrm{\cdot }{\mathrm{P}}_{\mathrm{V}}\right){\mathrm{P}}_{\mathrm{S}}$$

It can be seen that, according to this approach, the energy E _P actually absorbed by the preforms 3 increases in a linear or quasi-linear manner with the increase of the electric power P _S supplied to the sources 8, and conversely decreases linearly or quasi-linearly. linear with the increase of the electric power P _V supplied to the wind tunnel.

Thus configured and programmed, the machine 9 (and its method) makes it possible to introduce an automatic modification of the rate of the oven 4 while maintaining the quality of the containers 2. This results in a better adaptability of the oven 4 within the line of production, and the ability to vary the rate continuously during production, limiting the losses of non-compliant containers 2 .

Claims (11)

A method of manufacturing containers (2) from plastic blanks (3) , which comprises: - A phase of heating the blanks (3) parade, in a furnace (4) provided with a plurality of sources (8) of radiation, at a speed (V) of scrolling and according to a predetermined heating profile; a blow-molding phase of the blanks (3), within a blowing unit (5) , to form the containers (2), this method being characterized in that it comprises the following operations: a) changing the speed (V) of scrolling of the blanks (3); b) modify the heating profile; c) establishing, after a heating phase, a real thermal profile of at least one blank (3); d) performing, during the blowing phase, a pressure measurement in said blank (3) and detecting at least one point (B) singular pressure; e) measuring a first difference between the actual thermal profile of the blank (3) and a theoretical thermal profile, and a second difference between the singular point of pressure and a theoretical singular point; f) as long as the deviations are not both less than a respective predetermined tolerance, repeat steps b) to e); g) as long as the deviations are both less than the respective tolerance, and as long as the scroll speed (V) has not reached a predetermined end value, repeat steps a) to e). Process according to Claim 1, characterized in that the thermal profile comprises a thermography of the blank (3). Method according to claim 1 or claim 2, characterized in that the thermal profile comprises a temperature measurement performed on an outer wall (21) of the blank (3). Method according to one of claims 1 to 3, characterized in that the thermal profile comprises a temperature measurement performed on an inner wall (22) of the blank (3). Process according to one of Claims 1 to 4, characterized in that the singular point of pressure is a local pressure peak. Method according to one of claims 1 to 5, characterized in that the heating profile comprises an electric power (P _S ) delivered to the sources (8) of radiation. Method according to one of claims 1 to 6, characterized in that the heating profile comprises an electric power (P _V ) delivered to a ventilation system (19) of the oven (4). Computer program product intended to be stored in memory of a processing unit and / or stored on a memory medium readable by a reader of a processing unit, comprising instructions for carrying out operations a) to g ) a method according to one of claims 1 to 7. Machine (1) for the manufacture of containers (2) from blanks (3) of plastic, which comprises an oven (4) provided with a plurality of sources (8) of radiation, for heating at the parade of blanks (3) at a speed (V) of scrolling and according to a predetermined heating profile, characterized in that it comprises a control unit (9) programmed to effect a change in the speed (V) of scrolling and the profile heating according to a temperature measurement performed on a blank (3) at the outlet of the oven (4), and a pressure measurement performed in said blank (3) during a subsequent blowing. Machine (1) according to claim 9, characterized in that the control unit (9) is programmed to modify an electric power (P _S ) delivered to the sources (8). Machine (1) according to claim 9 or claim 10, characterized in that the control unit (9) is programmed to change an electric power (P _V ) delivered to a ventilation system (19) of the oven (4).

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